59 
heart wood, which has ceased to function, and to the fact that it 
very seldom “ rings ” a tree but goes up to the collar on one side 
only. 
In one field of rubber, 30 percent, of the trees were affected by 
the disease before its presence was even suspected. The disease is 
usually discovered earlier on wet lands as owing to the poor develop- 
ment of the root system, attacked trees blow over sooner. 
So far only one estate has had its young rubber badly attacked 
by Poria ; this is not because young trees are immune to attack, but 
because the laterals take time to establish contact. Isolated cases 
can of to.! be found on young rubber, and without doubt, many deaths 
formerly attributed to Pomes or brown root disease, were due to the 
then undescribed Poria. 
Treatment. 
With few exceptions treatment of individual trees is im- 
practicable, as the diseases are never discovered till too late. 
Attention must therefore be turned to prevention. 
Prevention. — Is of two kinds : (a) Total prevention of attacks ; 
(b) Prevention of spread from attacked areas. 
It has been shown that all the root parasites of Hevea also live 
on dead wood, i.e., can be saprophytes ; and that it is from dead 
wood that infections arise. The obvious remedy is to remove all 
dead timber and stumps both of jungle and Hevea trees, i.e., to 
adopt clean clearing : if this be done, it is not too much to say that 
immunity will be ensured from Brown root disease and Poria, while 
infections of Fames, Spluerostilbe , and TJstuUna will be reduced 
to those from spores blown or brought from neighbouring jungle 
or plantations. 
It is usual to find that saprophytic fungi, which become 
parasites, can only do so by gaining an entry through a “ wound,” 
and the results of inoculation experiments support this as applied 
to Hevea root diseases. It might be argued that if wounds could be 
avoided, i.e., by covering all laterals, the roots would be immune 
from attacks. Unfortunately a “ wound ” in the technical sense, 
includes any break in the protective covering of the plant. Such 
breaks may arise in many ways, of which the deaths of very small 
rootlets is one of the commonest. It follows that although exposed 
wounds of animal origin should be avoided as far as possible, because 
of the danger of spore infection, the root fungi cannot altogether be 
prevented from entering by such precautions. 
Before work was carried out on Poria and TJstuUna , it was 
thought that clean clearing was not essential, the idea being, that 
trees attacked by Fomes died in a relatively short time, so the 
presence of the disease would be discovered, and the source removed 
before neighbouring trees had time to establish contact. Also in the 
